Rotary offset duplicating machines include a master cylinder for supporting a master or planographic printing plate, a blanket cylinder for receiving an inked image from the master and an impression cylinder to transfer the inked image from the blanket cylinder to copy sheet. After the desired number of copies have been duplicated, the used master is removed or ejected from the master cylinder and replaced with a new master for a subsequent duplicating operation.
However, before commencing with a subsequent duplicating operation utilizing a new master, it is necessary to clean the blanket cylinder and remove the inked image deposited thereon from the previous master. This cleaning operation is normally performed by applying cleaning fluid to the blanket cylinder.
There are known devices for applying the cleaning fluid to the blanket cylinder for removing the inked image therefrom. One such device is shown in U.S. Pat. No. Re. 24,739 and includes a cleaning roller in engagement with a wick member supported in a reservoir containing cleaning fluid. As the cleaning roller is moved into rolling contact with the blanket cylinder, the cleaning roller transfers the cleaning fluid from the wick member to the blanket cylinder to remove the inked image therefrom.
Another device is disclosed in U.S. Pat. No. 3,693,547 and includes a cleaning roller in contact with a metering roller and a cylindrical wick. Cleaning fluid is transferred from the wick to the cleaning roller, and all of the rollers are movable as a unit to position the cleaning roller into and out of contact with the blanket cylinder. With the cleaning roller in cleaning contact with the blanket cylinder, the wick is held against rotation to provide a wiping or cleaning action to the cleaning roller. Thereafter, the wick is indexed to present a fresh portion thereof to the cleaning roller, and a jet of cleaning fluid is projected against the wick roller to clean its surface.
Another device is shown in U.S. Pat. No. 3,771,450 and includes a transfer roller, an axially oscillating "scrubbing" roller, both in contact with and rotating at the same surface speed as the blanket cylinder, and a metering roller in contact with both the transfer and the scrubbing rollers. Further, the device includes a wiper adapted to coact with the scrubbing roller to maintain it in a clean condition. Cleaning fluid is supplied to the rollers when they are in an operative cleaning position against the blanket cylinder and the wiper is in contact with the scrubbing roller, and the contaminated fluid is directed into a sump and carried to a collection container for subsequent disposal.
The prior art also exhibits blanket cleaners wherein there are cleaning rollers which are positively driven in a manner to produce realtive motion with respect to the blanket surface. Such devices are illustrated by U.S. Pat. Nos. 3,592,136 and 3,630,148 and British Pat. No. 1,169,668.
The blanket cleaners of the prior art worked reasonably well at a maintenance requirement level I which was adequate under many previously existing conditions where ink removal was the main consideration. Maintenance requirement level I is conceived of as a condition requiring some cleaning or treatment of the cleaner equipment by the operator, but no oftener than about once a day, e.g. 500 masters at maximum usage level. By contrast, a maintenance requirement level II is visualized as a condition in which the maintenance cleaning of the unit is required much less frequently. This would be an arrangement whereby the maintenance cleaning could be done at about 10,000 masters or more, no oftener than once a month so as to be at a frequency suited to a regular service call.
More importantly, however, a duplicating application may under some circumstances require cleaning and maintenance of the blanket cleaning unit several or even many times during a normal day's operation, when the cleaning units are of the types shown in the foregoing reference patents.
In this connection it is noted that with the advent of photoelectrostatic masters the environment changes somewhat. It was eventually found desirable, in order to have such masters print acceptably for runs which were as long as possible, to include in the moistening solution substantial quantities of additives such as glycerin (up to about 2% of glycerin for example).
With this change it was found that the existing blanket cleaning equipment represented by the prior art was no longer performing with sufficient effectiveness to be considered adequate maintenance requirement level I operation. The additives such as glycerin deposited upon the cleaning roller very rapidly, so that cleaning of the blanket cleaner equipment perhaps several or even many times a day became necessary in systems situations where many masters were run at few copies per master.
The foregoing situation consequently resulted in a highly undesirable frequency of clean-up of the blanket cleaner, and the time required to clean the unit was detracting seriously from the productivity of the equipment and the equanimity of the operator.